The present invention relates to a tie device, to tying apparatus and to methods for tying using said tie device, and in particular, to a tie device and apparatus and method which enables reinforcing bars or mesh, typically used in the construction industry, to be quickly and securely `tied`.
Concrete used in the building industry has a high resistance to compressive forces, but a relatively low tensile strength. Steel bars, on the other hand, have high tensile strength, so therefore it is common practice to reinforce the concrete with such steel bars to provide the necessary resistance to tension forces. In order to achieve the required strength of the resultant concrete member, the reinforcing bars need to be accurately positioned and retained in position whilst the concrete is being poured into the formwork. In many structural members, for example, slabs, beams, columns and walls, the steel bars are laid at right angles to each other to form a grid.
It is common practice to secure the bars, where they cross, by manually tying them together with tie wires, that is, by looping the wire around the bars and twisting the free ends of the wire together. Standard pliers, or pliers designed to facilitate the twisting of the wire, are used. This practice however has serious shortcomings. It is labour intensive and time consuming, resulting in significant direct costs. Indirect costs also result, since the next stage of construction cannot be started until the concrete structural component is completed. Additionally, because of the amount of kneeling and bending involved, particularly in large slab construction, injuries to the knees and backs of workers is commonplace.
There are no known machines on the market which will perform this work, although various unsatisfactory attempts have been made over the years to produce such a machine or tool.
For a wire tying tool to be useful and therefore accepted in the industry, it must be safe, reliable, convenient to use, and commercially attractive (i.e. reasonable price and effective in reducing overall costs).